Method and apparatus for performing power headroom reporting procedure in wireless communication system

ABSTRACT

A method and apparatus for performing a power headroom reporting (PHR) procedure in a wireless communication system is provided. A user equipment (UE) triggers at least one PHR, and determines whether the triggered at least one PHR is not cancelled. If it is determined that the triggered at least one PHR is not cancelled, the UE transmits a PHR.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisionalapplication No. 61/645,641 filed on May 11, 2012, and U.S. Provisionalapplication No. 61/677,451 filed on Jul. 30, 2012, all of which areincorporated by reference in their entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for performing a power headroomreporting (PHR) procedure in a wireless communication system.

2. Related Art

Universal mobile telecommunications system (UMTS) is a 3rd generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Transmit power needs to be properly regulated in order for a userequipment (UE) to transmit data to a base station (BS). When thetransmit power is too low, the BS may not be able to correctly receivethe data. When the transmit power is too high, even though the UE canreceive data without any problem, it may act as an interference toanother UE for receiving data. Therefore, the BS needs to optimize powerused in uplink transmission of the UE from a system aspect.

In order for the BS to regulate the transmit power of the UE, essentialinformation must be acquired from the UE. For this, power headroomreporting (PHR) of the UE is used. A power headroom implies power thatcan be further used in addition to the transmit power currently used bythe UE. That is, the power headroom indicates a difference betweenmaximum possible transmit power that can be used by the UE and thecurrently used transmit power. Upon receiving the PHR from the UE, theBS can determine transmit power used for uplink transmission of the UEat a next time on the basis of the received PHR. The determined transmitpower of the UE can be indicated by using a size of a resource block(RB) and a modulation and coding scheme (MCS), and can be used when anuplink (UL) grant is allocated to the UE at a next time. Since radioresources may be wasted if the UE frequently transmits the PHR, the UEcan define a PHR trigger condition and transmit the PHR only when thecondition is satisfied.

According to a PHR trigger condition, there may be a case where the UEcannot transmit the PHR in a specific situation. In this case, a methodof effectively determining a PHR trigger condition is required so thatthe UE can transmit the PHR.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for performing apower headroom reporting (PHR) procedure in a wireless communicationsystem. The present invention also provides a method for performing aPHR procedure if triggered PHR is not cancelled.

In an aspect, a method of performing, by a user equipment (UE), a powerheadroom reporting (PHR) procedure in a wireless communication system isprovided. The method includes triggering at least one PHR, determiningwhether the triggered at least one PHR is not cancelled, andtransmitting a PHR if it is determined that the triggered at least onePHR is not cancelled.

The triggered at least one PHR may comprise a first triggered PHR.

The PHR may be transmitted using a PHR media access control (MAC)control element (CE).

The PHR MAC CE may include an R field which is a reserved bit, and apower headroom field indicating a power headroom level.

The method may further include receiving uplink resources fortransmission.

The method may further include performing a logical channelprioritization (LCP) by considering the uplink resources for a PHR MACCE.

The method may further include determining whether the uplink resourcesfor transmission can accommodate the PHR MAC CE plus its subheader as aresult of the LCP.

The method may further include cancelling all triggered PHRs.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a radio frequency (RF) unit fortransmitting or receiving a radio signal, and a processor configured fortriggering at least one power headroom reporting (PHR), determiningwhether the triggered at least one PHR is not cancelled, andtransmitting a PHR if it is determined that the triggered at least onePHR is not cancelled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a wireless communication system.

FIG. 2 is a diagram showing a radio interface protocol architecture fora control plane.

FIG. 3 is a diagram showing a radio interface protocol architecture fora user plane.

FIG. 4 shows an example of a physical channel structure.

FIG. 5 shows an example of a PHR MAC CE.

FIG. 6 shows an example of a wideband system using carrier aggregationfor 3GPP LTE-A.

FIG. 7 shows an example of a structure of DL layer 2 when carrieraggregation is used.

FIG. 8 shows an example of a structure of UL layer 2 when carrieraggregation is used.

FIG. 9 shows an example of an extended PHR MAC CE.

FIG. 10 shows an example of a logical channel prioritization (LCP)procedure.

FIG. 11 shows an example of an operation process of a UE and a basestation in a contention-based random access procedure.

FIG. 12 shows an example of an operation process of a UE and that a basestation in a non-contention based random access procedure.

FIG. 13 shows an example of a method for performing a PHR procedureaccording to an embodiment of the present invention.

FIG. 14 shows another example of a method for performing a PHR procedureaccording to an embodiment of the present invention.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows a structure of a wireless communication system.

The structure of FIG. 1 is an example of a network structure of anevolved-UMTS terrestrial radio access network (E-UTRAN). An E-UTRANsystem may be a 3GPP LTE/LTE-A system. An evolved-UMTS terrestrial radioaccess network (E-UTRAN) includes a user equipment (UE) 10 and a basestation (BS) 20 which provides a control plane and a user plane to theUE. The user equipment (UE) 10 may be fixed or mobile, and may bereferred to as another terminology, such as a mobile station (MS), auser terminal (UT), a subscriber station (SS), a wireless device, etc.The BS 20 may be generally a fixed station that communicates with the UE10 and may be referred to as another terminology, such as an evolvednode-B (eNB), a base transceiver system (BTS), an access point, etc.There may be one or more cells within the coverage of the BS 20. Asingle cell may be configured to have one of bandwidths selected from1.25, 2.5, 5, 10, and 20 MHz, etc., and may provide downlink or uplinktransmission services to several UEs. In this case, different cells maybe configured to provide different bandwidths.

Interfaces for transmitting user traffic or control traffic may be usedbetween the BSs 20. The UE 10 and the BS 20 may be connected by means ofa Uu interface. The BSs 20 may be interconnected by means of an X2interface. The BSs 20 may be connected to an evolved packet core (EPC)by means of an S1 interface. The EPC may consist of a mobilitymanagement entity (MME), a serving gateway (S-GW), and a packet datanetwork (PDN) gateway (PDN-GW). The MME has UE access information or UEcapability information, and such information may be primarily used in UEmobility management. The S-GW is a gateway of which an endpoint is anE-UTRAN. The PDN-GW is a gateway of which an endpoint is a PDN. The MMEis in charge of functionality of a control plane. The S-GW is in chargeof functionality of a user plane. The BSs 20 may be connected to the MME30 by means of an S1-MME interface, and may be connected to the S-GW bymeans of an S1-U interface. The S1 interface supports a many-to-manyrelation between the BS 20 and the MME/S-GW 30.

Hereinafter, a downlink (DL) denotes communication from the BS 20 to theUE 10, and an uplink (UL) denotes communication from the UE 10 to the BS20. In the DL, a transmitter may be a part of the BS 20, and a receivermay be a part of the UE 10. In the UL, the transmitter may be a part ofthe UE 10, and the receiver may be a part of the BS 20.

FIG. 2 is a diagram showing a radio interface protocol architecture fora control plane. FIG. 3 is a diagram showing a radio interface protocolarchitecture for a user plane.

Layers of a radio interface protocol between the UE and the E-UTRAN areclassified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane whichis a protocol stack for control signal transmission and a user planewhich is a protocol stack for data information transmission. The layersof the radio interface protocol may exist in pairs at the UE and theE-UTRAN.

A physical (PHY) layer belonging to the L1 provides an upper layer withan information transfer service through a physical channel. The PHYlayer is connected to a medium access control (MAC) layer which is anupper layer of the PHY layer through a transport channel. Data may betransferred between the MAC layer and the PHY layer through thetransport channel. The transport channel may be classified according tohow and with what characteristics data is transmitted through a radiointerface. Or, the transport channel may be classified into a dedicatedtransport channel and a common transport channel depending on whether ornot to share the transport channel. Between different PHY layers, i.e.,a PHY layer of a transmitter and a PHY layer of a receiver, data may betransferred through the physical channel. The physical channel may bemodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

FIG. 4 shows an example of a physical channel structure.

A physical channel may consist of a plurality of subframes in a timedomain and a plurality of subcarriers in a frequency domain. Onesubframe may consist of a plurality of symbols in the time domain. Onesubframe may consist of a plurality of resource blocks (RBs). One RB mayconsist of a plurality of symbols and a plurality of subcarriers. Inaddition, each subframe may use specific subcarriers of specific symbolsof a corresponding subframe for a physical downlink control channel(PDCCH). For example, a first symbol of the subframe may be used for thePDCCH. A transmission time interval (TTI) which is a unit time for datatransmission may be equal to a length of one subframe.

A MAC layer belonging to the L2 provides a service to a higher layer,i.e., a radio link control (RLC), through a logical channel. A functionof the MAC layer includes mapping between the logical channel and thetransport channel and multiplexing/de-multiplexing for a transport blockprovided to a physical channel on a transport channel of a MAC servicedata unit (SDU) belonging to the logical channel. The logical channel islocated above the transport channel, and is mapped to the transportchannel. The logical channel may be divided into a control channel fordelivering information of the control plane and a traffic channel fordelivering information of the user plane.

An RLC layer belonging to the L2 supports reliable data transmission. Afunction of the RLC layer includes RLC SDU concatenation, segmentation,and reassembly. To ensure a variety of quality of service (QoS) requiredby a radio bearer (RB), the RLC layer provides three operation modes,i.e., a transparent mode (TM), an unacknowledged mode (UM), and anacknowledged mode (AM). The AM RLC provides error correction by using anautomatic repeat request (ARQ). Meanwhile, a function of the RLC layercan be implemented with a functional block inside the MAC layer. In thiscase, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. Afunction of a packet data convergence protocol (PDCP) layer in the userplane includes user data delivery, header compression, and ciphering.The header compression has a function for decreasing a size of an IPpacket header which contains relatively large-sized and unnecessarycontrol information, to support effective transmission in a radiosection having a narrow bandwidth. A function of a PDCP layer in thecontrol plane includes control-plane data delivery andciphering/integrity protection.

A radio resource control (RRC) layer belonging to the L3 is defined onlyin the control plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layerserves to control the logical channel, the transport channel, and thephysical channel in association with configuration, reconfiguration, andrelease of RBs. An RB is a logical path provided by the L2 for datadelivery between the UE and the network. The configuration of the RBimplies a process for specifying a radio protocol layer and channelproperties to provide a particular service and for determiningrespective detailed parameters and operations. The RB can be classifiedinto two types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRBis used as a path for transmitting an RRC message in the control plane.The DRB is used as a path for transmitting user data in the user plane.

A power headroom reporting (PHR) procedure of a user equipment isdescribed. It may be referred to 3GPP TS 36.321 V8.12.0.

The PHR procedure is used to provide the serving eNB with informationabout the difference between the nominal UE maximum transmit power andthe estimated power for uplink shared channel (UL-SCH) transmission. TheRRC controls the PHR by configuring the two timers periodicPHR-Timer andprohibitPHR-Timer, and by signalling dl-PathlossChange which sets thechange in measured downlink pathloss to trigger a PHR.

The PHR may be triggered if any of the following events occur:

-   -   prohibitPHR-Timer expires or has expired and the path loss has        changed more than dl-PathlossChange dB since the transmission of        a PHR when UE has UL resources for new transmission;    -   periodicPHR-Timer expires;    -   upon configuration or reconfiguration of the power headroom        reporting functionality by upper layers, which is not used to        disable the function.

If the UE has UL resources allocated for new transmission for this TTI,the UE may perform following operations:

-   -   if it is the first UL resource allocated for a new transmission        since the last MAC reset, start periodicPHR-Timer;    -   if the PHR procedure determines that at least one PHR has been        triggered since the last transmission of a PHR or this is the        first time that a PHR is triggered, and;    -   if the allocated UL resources can accommodate a PHR MAC control        element plus its subheader as a result of logical channel        prioritization:        -   obtain the value of the power headroom from the physical            layer;        -   instruct the multiplexing and assembly procedure to generate            and transmit a PHR MAC control element based on the value            reported by the physical layer;        -   start or restart periodicPHR-Timer;        -   start or restart prohibitPHR-Timer;        -   cancel all triggered PHR(s).

FIG. 5 shows an example of a PHR MAC CE.

The UE may transmit the PHR through the PHR MAC CE to the BS. The PHRMAC CE is identified by a MAC PDU subheader with LCID. The LCID may beallocated for the PHR MAC CE in the UL-SCH, and a value of the LCID maybe 11010. It has a fixed size and consists of a single octet defined asfollows:

-   -   R: reserved bit, set to “0”;    -   Power headroom (PH): this field indicates the power headroom        level. The length of the field is 6 bits, so total 64 power        headroom levels may be indicated. Table 1 shows the reported PH        and the corresponding power headroom levels.

TABLE 1 PH Power Headroom Level  0 POWER_HEADROOM_0  1 POWER_HEADROOM_1 2 POWER_HEADROOM_2  3 POWER_HEADROOM_3 . . . . . . 60 POWER_HEADROOM_6061 POWER_HEADROOM_61 62 POWER_HEADROOM_62 63 POWER_HEADROOM_63

A carrier aggregation (CA) of the 3GPP LTE-A is described.

The carrier aggregation implies a system that configures a wideband byaggregating one or more carriers having a bandwidth smaller than that ofa target wideband when the wireless communication system intends tosupport the wideband. The carrier aggregation can also be referred to asother terms such as a bandwidth aggregation system, or the like. Acarrier which is a target when aggregating one or more carriers candirectly use a bandwidth that is used in the legacy system in order toprovide backward compatibility with the legacy system. For example, the3GPP LTE can support a bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15MHz, and 20 MHz, and a 3GPP LTE-A can configure a wideband of 20 MHz orhigher by using only the bandwidth of the 3GPP LTE.

Meanwhile, the concept of a cell can be applied in the 3GPP LTE-A. Thecell is an entity configured by combining at least one unit of DLresources and selectively included UL resources from the perspective ofa UE. That is, one cell must include at least one unit of DL resources,but may not include UL resources. The one unit of DL resources may beone DL component carrier (CC). A linkage between a carrier frequency ofa DL resource and a carrier frequency of a UL resource can be indicatedby a system information block (SIB)-2 transmitted using the DL resource.Although a CC will be taken as an example in the following descriptionsof the present invention, it is apparent that the CC can be replacedwith a cell.

FIG. 6 shows an example of a wideband system using carrier aggregationfor 3GPP LTE-A.

Referring to FIG. 6, each CC has a bandwidth of 20 MHz, which is abandwidth of the 3GPP LTE. Up to 5 CCs may be aggregated, so maximumbandwidth of 100 MHz may be configured.

FIG. 7 shows an example of a structure of DL layer 2 when carrieraggregation is used. FIG. 8 shows an example of a structure of UL layer2 when carrier aggregation is used. The carrier aggregation may affect aMAC layer of the L2. For example, since the carrier aggregation uses aplurality of CCs, and each hybrid automatic repeat request (HARQ) entitymanages each CC, the MAC layer of the 3GPP LTE-A using the carrieraggregation shall perform operations related to a plurality of HARQentities. In addition, each HARQ entity processes a transport blockindependently. Therefore, when the carrier aggregation is used, aplurality of transport blocks may be transmitted or received at the sametime through a plurality of CCs.

A PHR procedure of a user equipment when the carrier aggregation is usedis described. It may be referred to 3GPP TS 36.321 V 10.5.0.

The PHR procedure is used to provide the serving eNB with informationabout the difference between the nominal UE maximum transmit power andthe estimated power for UL-SCH transmission per activated serving celland also with information about the difference between the nominal UEmaximum power and the estimated power for UL-SCH and PUCCH transmissionon a primary cell (PCell).

The RRC controls the PHR by configuring the two timers periodicPHR-Timerand prohibitPHR-Timer, and by signalling dl-PathlossChange which setsthe change in measured downlink pathloss and the required power backoffdue to power management to trigger a PHR.

The PHR may be triggered if any of the following events occur:

-   -   prohibitPHR-Timer expires or has expired and the path loss has        changed more than dl-PathlossChange dB for at least one        activated serving cell which is used as a pathloss reference        since the last transmission of a PHR when the UE has UL        resources for new transmission;    -   periodicPHR-Timer expires;    -   upon configuration or reconfiguration of the power headroom        reporting functionality by upper layers, which is not used to        disable the function;    -   activation of a secondary cell (SCell) with configured uplink;    -   prohibitPHR-Timer expires or has expired, when the UE has UL        resources for new transmission, and in this TTI, there are UL        resources allocated for transmission or there is a PUCCH        transmission on this cell, and the required power backoff due to        power management for this cell has changed more than        dl-PathlossChange dB since the last transmission of a PHR when        the UE had UL resources allocated for transmission or PUCCH        transmission on this cell, for any of the activated serving        cells with configured uplink.

Meanwhile, the UE should avoid triggering a PHR when the required powerbackoff due to power management decreases only temporarily (e.g. for upto a few tens of milliseconds) and it should avoid reflecting suchtemporary decrease in the values of P_(CMAX,c)/PH when a PHR istriggered by other triggering conditions.

If the UE has UL resources allocated for new transmission for this TTI,the UE may perform following operations:

-   -   if it is the first UL resource allocated for a new transmission        since the last MAC reset, start periodicPHR-Timer;    -   if the PHR procedure determines that at least one PHR has been        triggered since the last transmission of a PHR or this is the        first time that a PHR is triggered, and;    -   if the allocated UL resources can accommodate a PHR MAC control        element plus its subheader if extendedPHR is not configured, or        the extended PHR MAC control element plus its subheader if        extendedPHR is configured, as a result of logical channel        prioritization:        -   if extendedPHR is configured:            -   for each activated serving cell with configured uplink:                -   obtain the value of the type 1 power headroom;                -   if the UE has UL resources allocated for                    transmission on this serving cell for this TTI:                -    obtain the value for the corresponding P_(CMAX,c)                    field from the physical layer;            -   if simultaneousPUCCH-PUSCH is configured:                -   obtain the value of the type 2 power headroom for                    the PCell;                -   if the UE has a PUCCH transmission in this TTI:                -    obtain the value for the corresponding P_(CMAX,c)                    field from the physical layer;            -   instruct the multiplexing and assembly procedure to                generate and transmit an extended PHR MAC control                element based on the values reported by the physical                layer;        -   else:            -   obtain the value of the type 1 power headroom from the                physical layer;            -   instruct the multiplexing and assembly procedure to                generate and transmit a PHR MAC control element based on                the value reported by the physical layer;        -   start or restart periodicPHR-Timer;        -   start or restart prohibitPHR-Timer;        -   cancel all triggered PHR(s).

That is, the UE can report a PH to the BS with respect to all activatedserving cells. A PH for each serving cell can be determined as a valueremaining after subtracting an output value currently used in a specificserving cell from a maximum output value of the UE for the serving cell.If the PHR is triggered and a UL grant is allocated only some servingcells, the serving cells to which the UL grant is allocated cancalculate a PH by using the UL grant, and the remaining serving cellscan calculate a PH by using a pre-defined reference format. The maximumoutput value of the UE with respect to the serving cell is a valueexcluding a power reduction portion applicable within a range of amaximum power reduction (MPR) value. When calculating the maximum outputvalue of the UE, the power reduction portion may differ within the rangeof the MPR value according to an implementation of each UE. Therefore,in order to more correctly report the PHR, the UE can transmit the PHRby additionally including a maximum output value P_(CMAX,c) excludingthe power reduction portion.

A PHR MAC CE used for transmitting the PHR when the carrier aggregationis used may be the same as the PHR MAC CE shown in FIG. 5.

FIG. 9 shows an example of an extended PHR MAC CE.

The extended PHR MAC CE is identified by a MAC PDU subheader with LCID.It has a variable size. When type 2 PH is reported, the octet containingthe type 2 PH field is included first after the octet indicating thepresence of PH per SCell and followed by an octet containing theassociated P_(CMAX,c) field (if reported). Then follows in ascendingorder based on the ServCellIndex an octet with the type 1 PH field andan octet with the associated P_(CMAX,c) field (if reported), for thePCell and for each SCell indicated in the bitmap.

The extended PHR MAC CE is defined as follows:

-   -   C_(i): this field indicates the presence of a PH field for the        SCell with SCellIndex i. The C_(i) field set to “1” indicates        that a PH field for the SCell with SCellIndex i is reported. The        C_(i) field set to “0” indicates that a PH field for the SCell        with SCellIndex i is not reported;    -   R: reserved bit, set to “0”;    -   V: this field indicates if the PH value is based on a real        transmission or a reference format. For type 1 PH, V=0 indicates        real transmission on PUSCH and V=1 indicates that a PUSCH        reference format is used. For type 2 PH, V=0 indicates real        transmission on PUCCH and V=1 indicates that a PUCCH reference        format is used. Furthermore, for both type 1 and type 2 PH, V=0        indicates the presence of the associated P_(CMAX,c) field, and        V=1 indicates that the associated P_(CMAX,c) field is omitted;    -   Power headroom (PH): this field indicates the power headroom        level. The length of the field is 6 bits. Table 1 described        above shows the reported PH and the corresponding power headroom        levels.    -   P: this field indicates whether the UE applies power backoff due        to power management. The UE shall set P=1 if the corresponding        P_(CMAX,c) field would have had a different value if no power        backoff due to power management had been applied;    -   P_(CMAX,c): if present, this field indicates the P_(CMAX,c) or        {tilde over (P)}_(CMAX,c) used for calculation of the preceding        PH field. Table 2 shows the reported P_(CMAX,c) and the        corresponding nominal UE transmit power levels.

TABLE 2 P_(CMAX,c) Nominal UE transmit power level  0 PCMAX_C_00  1PCMAX_C_01  2 PCMAX_C_02 . . . . . . 61 PCMAX_C_61 62 PCMAX_C_62 63PCMAX_C_63

A logical channel prioritization (LCP) is described. It may be referredto 3GPP TS 36.321 V10.5.0.

In order to provide various types of services, at least one RB may beconfigured. A logical channel is allocated to a RB. A plurality oflogical channels corresponding to a plurality of RBs are multiplexed andtransmitted through one transport block (i.e. MAC PDU).

The LCP is a method for multiplexing data of the plurality of RBs (i.e.a plurality of logical channels) into a transport block (i.e. MAC PDU).LCP determines how much amount of given radio resources are allocated toeach of the plurality of RBs.

The LCP procedure is applied when a new transmission is performed. TheRRC controls the scheduling of uplink data by signalling for eachlogical channel: priority where an increasing priority value indicates alower priority level, prioritisedBitRate which sets the prioritized bitrate (PBR), and bucketSizeDuration which sets the bucket size duration(BSD). The priority may have a value between 1 and 8. The priorityhaving a value of 1 indicates the highest priority, and the priorityhaving a value of 8 indicates the lowest priority. The PBR indicates aminimum bit rate guaranteed for corresponding RB. That is, a bit rateindicated by the PBR is always guaranteed.

The UE shall maintain a variable Bj for each logical channel j. Bj shallbe initialized to zero when the related logical channel is established,and incremented by the product PBR×TTI duration for each TTI, where PBRis prioritized bit rate of logical channel j. However, the value of Bjcan never exceed the bucket size and if the value of Bj is larger thanthe bucket size of logical channel j, it shall be set to the bucketsize. The bucket size of a logical channel is equal to PBR×BSD, wherePBR and BSD are configured by upper layers.

The UE shall perform the following LCP procedure when a new transmissionis performed. The UE shall allocate resources to the logical channels inthe following steps.

-   -   Step 1: All the logical channels with Bj>0 are allocated        resources in a decreasing priority order. If the PBR of a radio        bearer is set to “infinity”, the UE shall allocate resources for        all the data that is available for transmission on the radio        bearer before meeting the PBR of the lower priority radio        bearer(s);    -   Step 2: The UE shall decrement Bj by the total size of MAC SDUs        served to logical channel j in Step 1. The value of Bj can be        negative.    -   Step 3: If any resources remain, all the logical channels are        served in a strict decreasing priority order (regardless of the        value of Bj) until either the data for that logical channel or        the UL grant is exhausted, whichever comes first. Logical        channels configured with equal priority should be served        equally.

The UE shall also follow the rules below during the schedulingprocedures above:

-   -   the UE should not segment an RLC SDU (or partially transmitted        SDU or retransmitted RLC PDU) if the whole SDU (or partially        transmitted SDU or retransmitted RLC PDU) fits into the        remaining resources;    -   if the UE segments an RLC SDU from the logical channel, it shall        maximize the size of the segment to fill the grant as much as        possible;    -   the UE should maximize the transmission of data.    -   if the UE is given an UL grant size that is equal to or larger        than 4 bytes while having data available for transmission, the        UE shall not transmit only padding BSR and/or padding (unless        the UL grant size is less than 7 bytes and an AMD PDU segment        needs to be transmitted).

The UE shall not transmit data for a logical channel corresponding to aradio bearer that is suspended.

A priority and/or a PBR of a logical channel of each RB are transmittedfrom a RRC layer of a network to a RRC layer of an UE through a RB setupmessage when the RB is initially configured. The RRC layer of the UEwhich receives the RB setup message configures a RB and sendsinformation on the LCP and the PBR of the logical channel of each RB tothe MAC layer of the UE. The MAC layer that receives the informationdetermines amounts of transmission data of the RB according to the LCPfor each TTI.

FIG. 10 shows an example of a logical channel prioritization (LCP)procedure.

Referring to FIG. 10, there are three RBs, i.e., an RB1 to which alogical channel of a highest priority P1 is mapped, an RB2 to which alogical channel of a second priority P2 is mapped, and an RB3 to which alogical channel of a lowest priority P3 is mapped. In addition, a PBR ofthe RB1 is a PBR 1, a PBR of the RB2 is a PBR 2, and a PBR or a RB3 is aPBR 3. First, a transmission data amount is determined according to datacorresponding to a PRB in each RB in a descending order of priority oflogical channels mapped to the RB1, the RB2, and the RB3. That is, thetransmission data amount can be determined to the PBR 1 in the RB1, thePBR 2 in the RB2, and the PBR 3 in the RB3. Since there are remainingradio resources even if a transmission data amount corresponding to thePBR in each RB is fully allocated, the remaining radio resources can beallocated to the RB1 having the highest priority.

For the LCP procedure, the UE shall take into account the followingrelative priority in decreasing order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

When the UE is requested to transmit multiple MAC PDUs in one TTI, steps1 to 3 and the associated rules may be applied either to each grantindependently or to the sum of the capacities of the grants. Also theorder in which the grants are processed is left up to UE implementation.It is up to the UE implementation to decide in which MAC PDU a MACcontrol element is included when UE is requested to transmit multipleMAC PDUs in one TTI.

A random access procedure is described.

The UE can perform a random access procedure in the following cases.

-   -   When the UE performs an initial access to the BS in a situation        where there is no RRC connection with the BS.    -   When the UE initially accesses to a target cell in a handover        procedure.    -   When it is requested by a command of the BS.    -   When data to be transmitted in an uplink is generated in a        situation where uplink time misalignment occurs or a designated        radio resource used to request a radio resource is not        allocated.    -   When a recovery process is performed at the occurrence of a        radio link failure or a handover failure.

In an LTE system, a non-contention based random access procedureallocating, by a BS, a designated (or dedicated) random access preambleto a particular UE and randomly accessing, by the UE, with the randomaccess preamble is provided. In other words, the procedure of selectinga random access preamble includes a contention based random accessprocedure that a UE randomly selects one random access preamble from aparticular set and uses the same and a non-contention based randomaccess procedure that a UE uses a random access preamble allocatedthereto. A difference between the two random access procedures lies in ageneration of collision due to contention as described hereinafter. Thenon-contention based random access procedure may be used only when theforegoing handover process is performed or when it is requested by acommand from a BS.

FIG. 11 shows an example of an operation process of a UE and a basestation in a contention-based random access procedure.

1. In the contention based random access, a UE randomly selects onerandom access from a set of random access preambles indicated by systeminformation or a handover command, selects a PRACH resource able totransmit the random access preamble, and transmits the same.

2. After the random access preamble is transmitted, the UE attempts toreceive a random access response thereof within a random access responsereception window indicated by the system information or the handovercommand. In detail, the random access response information istransmitted in the form of a MAC PDU, and the MAC PDU is transferred ona PDSCH. In order to allow the UE to properly receive the informationtransmitted on the PDSCH, a PDCCH is also transferred together. Namely,the PDCCH includes information regarding a UE which is to receive thePDSCH, frequency and time information of radio resource of the PDSCH, atransmission format of the PDSCH, and the like. When the UE successfullyreceives the PDCCH destined therefor, the UE appropriately receives therandom access response transmitted on the PDSCH according to theinformation items of the PDCCH. The random access response includes arandom access preamble identifier (ID), a UL grant (uplink radioresource), a temporary C-RNTI, and a time alignment command (TAC). Inthe above, the reason why the random access preamble identifier isrequired is because, since a single random access response may includerandom access response information for one or more UEs, so the randomaccess preamble identifier informs for which UE the UL grant, temporaryC-RNTI, and TAC are valid. The random access preamble identifier isidentical to a random access preamble selected by the UE in 1.

3. When the UE receives the random access response valid therefor, theUE processes the information items included in the random accessresponse. Namely, the UE applies the TAC and stores the temporaryC-RNTI. Also, the UE transmits data stored in a buffer thereof or newlygenerated data to the BS by using the UL grant. In this case, anidentifier of the UE should be included in the data included in the ULgrant. The reason is because, in the contention based random accessprocedure, the BS cannot determine which UEs perform the random accessprocedure, so in order to resolve collision later, the BS shouldidentify UEs. Also, there are two types of methods for including anidentifier of the UE. A first method is that when the UE has a validcell identifier already allocated in the corresponding cell before therandom access procedure, the UE transmits its cell identifier throughthe UL grant. Meanwhile, when the UE has not been allocated a valid cellidentifier before the random access procedure, the UE includes itsunique identifier (e.g., an S-TMSI or a random ID) in data and transmitsthe same. In general, the unique identifier is longer than a cellidentifier. When the UE transmits the data through the UL grant, the UEstarts a contention resolution timer.

4. After the UE transmits the data including its identifier through theUL grant included in the random access response, the UE waits for aninstruction from the BS for a collision resolution. Namely, in order toreceive a particular message, the UE attempts to receive a PDCCH. Thereare two methods for receiving a PDCCH. As mentioned above, when theidentifier of the UE transmitted through the UL grant is a cellidentifier, the UE attempts to receive a PDCCH by using its cellidentifier, and when the identifier is a unique identifier, the UEattempts to receive a PDCCH by using the temporary C-RNTI included inthe random access response. Thereafter, in the former case, when a PDCCHis received through its cell identifier before the contention resolutiontimer expires, the UE determines that the random access procedure hasbeen normally performed, and terminates the random access procedure. Inthe latter case, when the UE receives a PDCCH through the temporary cellidentifier before the contention resolution time expires, the UE checksdata transferred by the PDSCH indicated by the PDCCH. When the datacontent includes its unique identifier, the UE determines that therandom access procedure has been normally performed, and terminates therandom access procedure.

FIG. 12 shows an example of an operation process of a UE and that a basestation in a non-contention based random access procedure. Additionally,in comparison to the contention based random access procedure, in thenon-contention based random access procedure, upon receiving randomaccess response information, it is determined that a random accessprocedure has been normally performed, and the random access procedureis terminated.

1. As mentioned above, the non-contention based random access proceduremay exist, first, in the case of a handover process, and second, in thecase of being requested by a command from a BS. Of course, in the twocases, the contention based random access procedure may be performed.First, for the non-contention based random access procedure, it isimportant to receive a designated random access preamble eliminating apossibility of collision. A method of receiving an indication of therandom access preamble includes a handover command and a PDCCH command.

2. After receiving the allocated random access preamble designated onlyfor the UE, the UE transmits the preamble to the BS.

3. A method of receiving random access response information is the sameas that in the contention-based random access procedure.

As described above, a PHR is transmitted when specific conditions aremet. When the UE receives a UL grant from the BS, the UE checks whethera MAC PDU indicated by the UL grant can include a PHR MAC CE as a resultof a LCP procedure. That is, provided that the UE has the UL grant thatcan accommodate the PHR MAC CE, the PHR is transmitted by including thePHR MAC CE in the MAC PDU if one of the following two conditions is met.

-   -   At least one PHR has been triggered since the last transmission        of a PHR, or    -   This is the first time that a PHR is triggered

However, with the current PHR procedure, a following scenario mayhappen.

-   -   The first PHR is triggered since the RRC connection        establishment.    -   The UE receives the first UL grant after the first PHR is        triggered. It is assumed that the first received UL grant cannot        accommodate a PHR MAC CE as a result of the LCP procedure. For        example, when the UL grant may indicate a MAC PDU having a size        of 56 bits, the MAC PDU may include 16 bits C-RNTI MAC CE        including 8 bits MAC subheader and 24 bits long BSR MAC CE        including 8 bits MAC subheader. In this case, the MAC PDU cannot        accommodate the PHR MAC CE according to priorities of data as a        result of the LCP procedure.    -   Consequently, the transmission of the PHR cannot be made and the        first triggered PHR remains not cancelled.    -   The second PHR is triggered before the second UL grant.    -   The second UL grant that is large enough to accommodate the PHR        MAC CE is received.

In this scenario, though there are triggered PHRs (i.e., the first andsecond PHRs) that have not yet been cancelled and there is the second ULgrant that can accommodate the PHR MAC CE, the UE cannot make, accordingto the current PHR procedure, the transmission of the PHR at the laststep of the above scenario because:

-   -   There is not the last transmission of the PHR, i.e., any PHR has        not be transmitted since the RRC connection establishment, nor    -   This is not the first time that a PHR is triggered, i.e., it is        the second time.

Even if the PHRs are continuously triggered, and the UE receives ULgrants which can include the PHR MAC CE, the UE cannot transmittriggered PHR. As a result, the triggered PHR cannot be transmitted, andthe transmission of the PHR may be stuck.

The PHR stuck problem described above may happen during a handoverprocedure as follows.

-   -   The UE establishes the RRC connection with the eNB that is not        using the PHR functionality. Note that the PHR functionality is        currently optional.    -   E.g., upon the UE's movement, the UE receives the handover        command including MAC-MainConfig including phr-Config.    -   The UE reconfigures MAC-MainConfig, which triggers a PHR for the        first time.    -   The UE is asked to perform a contention based RA procedure        toward the target cell.    -   The UE receives the first UL grant (56 bits) in the RA response.    -   The UE starts periodicPHR-Timer with short value, e.g., 10 or 20        ms.    -   The UE generates a MAC PDU just including 24 bits C-RNTI MAC CE        including MAC subheader and 32 bits long BSR MAC CE including        MAC subheader as a result of the LCP procedure. Therefore, the        PHR cannot be transmitted, which means there is no PHR        transmission.    -   periodicPHR-Timer expires, which triggers a PHR for the second        time.    -   The UE receives the second UL grant.    -   Though the UE receives the second UL grant that is large enough        to accommodate the PHR MAC CE, the UE cannot transmit the PHR        because the UE never meets the aforementioned conditions        considering it is the second time that a PHR is triggered and no        transmission of a PHR is made yet.

Here, a method for performing a PHR procedure when the PHR stuck problemmay happen according to an embodiment of the present invention isdescribed.

To avoid the PHR stuck problem if it is considered an issue, variousapproaches could be basically possible. For example, to rely on the eNBcontrol to make sure that e.g. in the aforementioned handover scenario,the UE may be provided with the second UL grant before the second PHR istriggered by e.g., avoiding small values of periodicPHR-Timer. However,considering that the completion time of a contention based random accessprocedure is not predictable, we consider the PHR stuck problem asunavoidable even if we rely on the smart eNB control. Also, theconsequence to this situation would seem severe because there is nomeans to solve except the RRC connection release. Accordingly, thechange of conditions for transmitting triggered PHR may be needed.

Therefore, it is proposed that the in the above scenario, a UE cantransmit the first triggered PHR in the next UL grant that canaccommodate the PHR MAC CE or extended PHR MAC CE after the first ULgrant that cannot accommodate the PHR MAC CE or extended PHR MAC CE ifat least one PHR has been triggered and not cancelled. That is, the UEmay transmit the PHR which is triggered but not cancelled. If there isnot triggered PHR not cancelled, the UE does not transmit the PHR to theBS. If multiple PHRs are triggered, and there is at least one triggeredPHR not cancelled, the UE may transmit the triggered PHR to the BS.

FIG. 13 shows an example of a method for performing a PHR procedureaccording to an embodiment of the present invention.

1. A UE receives a PHR configuration from a BS. A PHR procedure may beconfigured by the PHR configuration. The PHR configuration may bereceived through an RRC connection reconfiguration message. A PHR istriggered according to the PHR configuration by the UE.

2. The UE receives a first UL grant from the BS. The first UL grant maybe received through a PDCCH or a random access response message.

3. The UE configures a first MAC PDU by the first UL grant as a resultof an LCP procedure. The UE checks whether the first MAC PDU indicatedby the first UL grant can include a PHR MAC CE or not. It is assumedthat the first MAC PDU does not include a PHR MAC CE because of a sizeof the first MAC PDU and priorities of data to be transmitted. The UEtransmits the configured first MAC PDU to the BS.

The PHR MAC CE may be an extended PHR MAC CE if the extended PHR MAC CEis configured. The BS may configure the extended PHR MAC CE to the UE.In addition, if the extended PHR MAC CE is configured, the UE may checkwhether the MAC PDU indicated by the received UL grant can include theextended PHR MAC CE or not. If the extended PHR MAC CE is notconfigured, the UE may check whether the MAC PDU indicated by thereceived UL grant can include the PHR MAC CE or not.

4. The UE receives a second UL grant from the BS. The second UL grantmay be received through a PDCCH or a random access response message. Itis assumed that a second MAC PDU, configured by the second UL grant, caninclude a PHR MAC CE as a result of the LCP procedure. The UE checks ifat least one PHR has been triggered but not cancelled.

5. In FIG. 13, there is a PHR triggered but not cancelled. Accordingly,the UE configures the second MAC PDU including the PHR MAC CE, andtransmits the second MAC PDU to the BS. The UE cancels all triggeredPHRs.

6. The UE receives a third UL grant from the BS. The third UL grant maybe received through a PDCCH or a random access response message. It isassumed that a third MAC PDU, configured by the third UL grant, caninclude a PHR MAC CE as a result of the LCP procedure. The UE checks ifat least one PHR has been triggered but not cancelled.

7. It is assumed that additional PHR is not triggered since alltriggered have been canceled in step 5. Accordingly, the UE configuresthe third MAC PDU not including the PHR MAC CE, and transmits the thirdMAC PDU to the BS.

Accordingly, the UE may perform following operations according to anembodiment of the present invention if the UE has UL resources allocatedfor new transmission for this TTI.

-   -   if it is the first UL resource allocated for a new transmission        since the last MAC reset, start periodicPHR-Timer;    -   if the PHR procedure determines that at least one PHR has been        triggered and not cancelled, and;    -   if the allocated UL resources can accommodate a PHR MAC control        element plus its subheader as a result of logical channel        prioritization:        -   obtain the value of the power headroom from the physical            layer;        -   instruct the multiplexing and assembly procedure to generate            and transmit a PHR MAC control element based on the value            reported by the physical layer;        -   start or restart periodicPHR-Timer;        -   start or restart prohibitPHR-Timer;        -   cancel all triggered PHR(s).

FIG. 14 shows another example of a method for performing a PHR procedureaccording to an embodiment of the present invention.

At step S100, the UE triggers at least one PHR. At step S110, the UEdetermines whether the triggered at least one PHR is not cancelled. Ifit is determined that the triggered at least one PHR is not cancelled,at step S120, the UE transmits a PHR.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

An eNB 800 may include a processor 810, a memory 820 and a radiofrequency (RF) unit 830. The processor 810 may be configured toimplement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 810. The memory 820 is operatively coupledwith the processor 810 and stores a variety of information to operatethe processor 810. The RF unit 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

According to the present invention, in a situation that the PHR stuckproblem may occur according to the current PHR procedure, the PHR can betransmitted.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method of performing, by a user equipment (UE),a power headroom reporting procedure in a wireless communication system,the method comprising: triggering a first power headroom report (PHR);determining that a first allocated uplink (UL) resource cannotaccommodate a PHR media access control (MAC) control element (CE) plusits subheader; triggering a second PHR; determining whether at least onePHR has been triggered and not cancelled, determining whether a secondallocated UL resource can accommodate the PHR MAC CE plus its subheader;and transmitting the PHR MAC CE if it is determined that the at leastone PHR has been triggered and not canceled, and that the secondallocated UL resource can accommodate the PHR MAC CE plus its subheader.2. The method of claim 1, wherein the PHR MAC CE includes an R fieldwhich is a reserved bit, and a power headroom field indicating a powerheadroom level.
 3. The method of claim 1, further comprising receivinguplink resources for transmission.
 4. The method of claim 3, furthercomprising performing a logical channel prioritization (LCP) byconsidering the uplink resources for the PHR MAC CE.
 5. The method ofclaim 1, further comprising cancelling all triggered PHRs.
 6. The methodof claim 1, wherein the PHR MAC CE is an extended PHR MAC CE.
 7. Themethod of claim 1, further comprising receiving a PHR configuration froma base station (BS).
 8. A user equipment (UE) in a wirelesscommunication system, the UE comprising: a radio frequency (RF) unitconfigured to transmit or receive a radio signal; and a processoroperably coupled with the RF unit and configured to: trigger a firstpower headroom report (PHR), determine that a first allocated uplink(UL) resource cannot accommodate a PHR media access control (MAC)control element (CE) plus its subheader, trigger a second PHR, determinewhether at least one PHR has been triggered and not cancelled, determinewhether a second allocated UL resource can accommodate the PHR MAC CEplus its subheader, and transmit the PHR MAC CE if it is determined thatthe at least one PHR has been triggered and not canceled, and that thesecond allocated UL resource can accommodate the PHR MAC CE plus itssubheader.
 9. The UE of claim 8, wherein the processor is furtherconfigured to determine whether uplink resources for transmission canaccommodate the PHE MAC CE plus its subheader as a result of a logicalchannel prioritization (LCP).
 10. The UE of claim 8, wherein theprocessor is further configured to cancel all triggered PHRs.